This invention relates to an improvement of an alternate sweeping system for use in an oscilloscope.
An alternate sweeping system has been used for a high grade oscilloscope for the purpose of displaying a waveform along an enlarged or expanded time axis. According to the alternate sweeping system a sweeping signal having a large signal width and a delayed sweeping signal having a small signal width are alternately applied to the horizontal deflection circuit of a cathode ray tube so as to alternately display a waveform with a not enlarged time axis and a waveform with an enlarged time axis.
FIG. 1 diagrammatically shows such manner of display of a pulse signal, for example, in which A shows a waveform caused by a not delayed sweeping signal and B a waveform caused by a delayed sweeping signal. A thick line portion of A is enlarged as shown in B.
However, the waveform caused by the delayed sweeping signal has a time axis enlarged more than several ten times of that of the waveform caused by the not delayed sweeping signal so that when sweeping with the delayed sweeping signal, the time required for an electron beam to impinge upon the fluorescent screen of the cathode ray tube is shortened with the result that the quantity of light emitted at bright lines decreases, thus making it difficult to observe the waveform caused by the delayed sweeping signal.
This phenomenon results in the following disadvantage. More particularly, where an image signal waveform is to be observed, a waveform of one frame is displyed by a not delayed sweeping signal, while a waveform for an interval of 1H (an interval between the beginning of one horizontal scanning line and the beginning of the next horizontal scanning line) is displayed with a delayed scanning signal. In this case, as the ratio of enlargement of the time axes becomes large, the quantity of light emitted by bright lines of the waveform displayed for 1H decreases greatly, thereby not only making difficult to observe visually the displayed waveform but also making it impossible to photograph the displayed waveform.